Metal stents are commonly fabricated from stainless steel or nitinol sheet metal or tubing. Radiopacity of the bare metal stent is determined by the radiographic density of the stent material and the thickness of the stent wall. For small diameter stents such as coronary stents and other stents with a diameter of less than 12 mm, the bare metal stents may not necessarily have enough radiopacity for imaging purposes.
There are a number of different methods for providing and enhancing radiopacity in stents. One method of enhancing stent radiopacity involves depositing a thin surface layer of more radiographically dense material such as gold on the surface of the stent. The layer may be deposited via plating, ion deposition or any other suitable technique. Deposition methods, however, may be frustrated by poor adhesion and the resultant delamination of the deposited layer. Furthermore, the deposited layer may affect stent properties and biocompatibility adversely if it has low elongation properties or contains impurities.
Another method for providing radiopacity in stents such as wire stents is to make the stent wire of a composite construction with a radiographically dense core material such as tantalum or platinum and a casing of structural material such as stainless steel or Elgiloy.
Another method for providing a stent with radiopacity is to add an immiscible highly radiopaque agent in with the stent metal during ingot melting. With this method, however, the radiopaque constituent may be drawn out to a stringer morphology during sheet metal or tubing fabrication and become a structural weakpoint within the material.
Yet another method for providing a stent with radiopacity involves providing a radiopaque plug of material in the stent. Typically, the stent will be provided with one or more openings in which the radiopaque material is inserted.
There remains a need for novel methods of providing radiopacity in stents which do not have the adhesion problems associated with plating and which do not change the metallurgy of the base metal of the stent.
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